a  CDS/NTDS  that  normally  uses  a  three-bay/one-bay computer  configuration  to  operate  at  full  capability. Because of a casualty to the one bay, that bay is dropped offline. The CDS/NTDS can still perform its basic mission, but the system is reduced because not all four computers are being used. Devices that are used to bring the computer to reduced capability are switchboards and computer control panels. The operational program (software) must also be reconfigured to reflect the hardware reconfiguration. This can be accomplished at an I/O device using operating system functions (commands). Again refer to the SOMs or CSTOMs for exact details of your system’s capabilities and limitations and the hardware and software required to reconfigure it. OPERATIONAL REQUIREMENTS OF COMPUTER  SYSTEMS Effective  operation  of  computer  systems  also depends  on  security  and  on  controlling  electromagnetic disturbances. You’ll need to pay particular attention to ADP security and electromagnetic interference (EMI). Lack  of  attention  to  these  factors  can  seriously jeopardize  the  security  and  operation  of  a  computer system. ADP Security The     security     of     computers     depends     on administrative   and   physical   controls. The administrative   requirements   (directives   and instructions) will provide the policy and procedures to follow  to  meet  the  physical  requirements.  Let’s highlight some of the things you will handle on a regular basis that require protection to ensure the security of the computer system. Data and information —For tactical and tactical support  systems,  the  data  the  computer  handles  and makes available is classified. (Includes COMSEC material for tactical data links). Passwords  —Used with nontactical systems (SNAP) to ensure only authorized users gain access to the computer system. Operational   programs on magnetic tape, disk, and  disk  packs—For  tactical  and  tactical  support systems, these programs and any revisions (program patches)  are  classified.  For  nontactical  systems,  the operational programs may be copyrighted and require protection to avoid misuse. 1-14 Safe   combinations  —For  controlled  spaces where computers are used. Computers —Computers must be safeguarded; they are an ADP asset. Be sure you know where the emergency destruction procedures for the computer system are. They should be readily available. For more detailed information on guidelines that will aid in the security of computers, refer to OPNAVINST 5239.1, Department of the Navy Security Program for Automatic Data Processing Systems and OPNAVINST 5510.1,  Department of the Navy  Information  and  Personnel  Security  Program Regulation. Electromagnetic  Interference Electromagnetic   interference   (EMI)   is   an electromagnetic  or  electrostatic  disturbance  that  causes electronic equipment to malfunction or to produce undesirable responses or conditions that do not meet the requirements of interference tests. You must be more aware of the problems EMI causes and the solutions required  to  resolve  these  problems.  No  magic  is involved  in  reducing  or  eliminating  EMI.  Everyday common  sense  approaches  to  maintaining  equipment will resolve many problems caused by EMI. TYPES OF EMI.  —There  are  three  types  of EMI—natural, inherent, and manmade. Natural EMI. —Natural interference is caused by natural events, such as snowstorms, electrical storms, rain particles, and solar radiation. It can cause problems with rf data links between shore, ship, and air, but few problems with modem digital data equipment. Inherent EMI.  —Inherent  interference  is  noise within a piece of electronic equipment and is caused by thermal agitation or electrons flowing through circuit resistance. Manmade EMI. —Manmade EMI is produced by a number of different classes of electrical and electronic equipment. The equipment includes, but is not limited to, transmitters, welders, power lines, motors and generators,  lighting,  engines  and  igniters,  and  electrical controllers. A number of these devices can cause severe EMI, which can degrade the operation of shipboard and shorebased computer systems. EMI can be classified by its spectrum distribution. It can be either broadband or narrowband interference. These  terms  refer  to  the  frequency  spectrum  the interference covers.